The present invention relates to a patient weighing scale, more specifically, to a scale which will provide an automatic display of the patient's weight without the need for any mechanical adjustments during the weighing.
U.S. Pat. No. 3,032,131 describes an elevation adjustable weighing scale for patients which is constructed as a fork lift for adjusting the elevational position of the weighing platform. This known weighing scale includes a mechanical weighing mechanism and is intended for weighing bedridden patients. However, difficulties are encountered in getting the patient onto the platform, especially when the patient is connected to various other medical devices, for example, intravenous feeding means or the like.
In the known device it is necessary to turn the patient on his side and somehow roll him onto the platform if he is to be weighed in a lying down position. Moreover, the nurse must make the mechanical adjustments necessary for ascertaining the weight.
It is also known to employ transducers responsive to stress or pressure loads in connection with weighing mechanisms. Thus, it is known to place one transducer under each of the four legs of a patient's bed. This method has the advantage that the patient does not need to be moved at all. However, the dead weight of the bed and other equipment must be taken into account in order to ascertain the true weight of the patient and this may reduce the accuracy of the ascertained weight, especially since humidity and other factors may change the dead weight.
There are also known in the art various mechanisms for supporting a patient. For example, U.S. Pat. No. 2,544,593 discloses a carriage and lift apparatus for patients, wherein a stretcher may be raised and lowered by mechanical means. Similarly, U.S. Pat. No. 2,792,052 describes an invalid walker and transfer device also capable of manipulating a stretcher, U.S. Pat. No. 3,469,269 describes hospital and ambulance patient handling equipment, wherein the patient may be secured in a sitting harness suspended from a boom. The just described devices are not suitable for weighing a patient.
U.S. Pat. No. 2,866,059 describes a transducer responsive to vertical forces which would be suitable for the present purposes. Such transducers provide electrical signals which are a direct measure of the forces or rather vertical forces involved.
U.S. Pat. Nos. 3,795,284 and 3,876,018 describe patient weighing devices in which a pressure transducer and digital read-out means are used. The entire structure is, however, rather complicated since the weighing structure is integrated into the structure of a hospital bed.